1. Field of the Invention
The present invention relates to a directional backlight, a display apparatus and a stereoscopic display apparatus using the directional backlight.
2. Description of the Related Art
Various systems for implementing stereoscopic display apparatuses, or three-dimensional (3D) image display apparatuses, capable of displaying three-dimensional moving images are known. In recent years, demands for stereoscopic display systems that use a flat panel and do not require special glasses have been increased particularly. A relatively easily implementable system that provides a parallax creating unit is known. The parallax creating unit is provided in immediate front of a display panel (display device) whose pixels are positionally fixed, and controls directions of light rays emitted from the display panel toward an observer. Examples of such a display panel include direct-view type and projection type liquid crystal displays and plasma displays.
The parallax creating unit is generally called a parallax barrier, and controls light rays such that an observer sees different views from different viewing angles even when the image viewed by the observer is at same locational position on a light-ray control device. Specifically, to create only lateral parallax (horizontal parallax), a slit sheet or a lenticular sheet (cylindrical lens array) is employed as the parallax creating unit. To create longitudinal parallaxes (vertical parallaxes) in addition to horizontal parallax, a pinhole array or a lens array is used as the parallax creating unit.
Systems that use a parallax barrier are further classified into a binocular display, a multi-view display, a super multi-view display (multi-view display using a super multi-view condition), and integral imaging (hereinafter, IP system, which is an abbreviation of integral photography). The basic principle of these systems is substantially identical with that was invented about 100 years ago and has been used in stereophotography.
As described in Journal of the Optical Society of America A, Vol. 15, No. 8, pp. 2059-2065 (1998) and in JP-A 2006-267928 (KOKAI), in the multi-view display and the one-directional (1D) IP system (horizontal-parallax-only IP system), a trade-off relation among three properties; that is, parallax, resolution, and apparent depth makes it difficult to attain adequate levels in all the three properties. To solve this problem, techniques for improving resolution by changing directions of light rays using time-division control are proposed in Japanese Patent No. 3585781 and Japanese Patent No. 3710934.
However, these conventional techniques are disadvantageous in that increasing the number of directions of light rays and decreasing the number of light sources to be switched by the time-division control are not favorably compatible, which makes it difficult to respond to changes in viewing location.